1. Field of the Invention
The invention relates to a substrate processing unit for processing, for example, a semiconductor wafer, a substrate for use in liquid crystal display, a substrate for use in a storage disc, a substrate for use in a mask and such other substrates.
2. Description of the Prior Art
In a method of fabricating a semiconductor, a wafer is processed by utilizing a chemical fluid such as purified water in order to cleanse the surface of the wafer. For example, Japanese Patent Publication No. 6-103686 discloses a surface dry processing method including a process of supplying dry vapor to form a fluid layer of a dry fluid over a cleaning fluid, and a process of replacing the cleaning fluid with a fluid layer by directly replacing the cleaning fluid with dry fluid from the surface of a material to be dried such as a wafer, wherein the surface of the material to be dried is substantially of the same temperature as that of the vapor when contacting the vapor, and the replacement of the cleaning fluid by the dry fluid is sufficiently slow in the manner that fluid droplets do not remain on the material to be dried so that no part of the cleaning fluid or dry fluid which would have been removed by the vaporization of the fluid droplets substantially remains.
Meanwhile, Japanese Patent No. 3,009,699 discloses a method of processing a surface of a substrate (hereinafter referred to as xe2x80x9cSubstrate Surfacexe2x80x9d) for separating fluid from a substrate such as a semiconductor wafer and the like after the substrate is immersed in a fluid bath, and allowing the fluid and the substrate surface to directly contact the vapor of an organic compound while the substrate is separated from the fluid. This method has a vapor pressure under which an organic compound vapor is not saturated at the temperature of the substrate, and the vapor is not condensed on the substrate during the separation of the substrate from the fluid, wherein the organic compound is soluble in the fluid and is selected from a group of organic compounds which lower the surface tension when they are soluble in the fluid. The vapor pressure of the organic compound, solubility of the organic compound relative to the fluid, and the speed of separation of the substrate from the fluid are selected to have a direction and magnitude such that no part of the fluid substantially remains on the substrate during the separation of the substrate from the fluid and an inclination is provided on the surface tension of the fluid when the substrate crosses the surface of the fluid.
The applicant of the present application has developed and proposed many methods of processing a semiconductor wafer and the like, and has obtained letters patent such as those disclosed in Japanese Patent No. 3,017,033, U.S. Pat. No. 5,951,779 and Japanese Application No. 11-183469.
Japanese Patent No. 3,017,033 discloses a method of processing or a series of processes whereby a material in a sealed container is to be dried from a cleaning process to a drying process, wherein processing from the final cleaning to steam drying can be carried out in one container, and the organic solvent is vaporized at a low temperature in the range of 35xc2x0 C. to 60xc2x0 C. and the material is dried by the vapor thus generated.
Japanese Patent No. 5,951,779 discloses a method of processing or a series of processes whereby a material in a sealed container is to be dried through a steam drying process following a cleaning process, in the manner stated below.
That is, the method includes (1) a step of supplying hot purified water to the inner sides of a container in which the material to be dried is accommodated; (2) a step of supplying organic solvent steam to the space above the hot purified water in the container after the final cleaning processing is carried out; (3) a step of continuously supplying an inert gas from the upper side of the container while sucking and discharging the hot purified water from the bottom side of the container after the supply of the organic solvent is stopped; and (4) a step of continuously sucking the hot purified water to depressurize the container so as to dry the material to be dried after the completion of sucking and discharging the hot purified water, wherein a degree of depressurization of the container is controlled and maintained at a predetermined set value to subject the material to be dried to dry processing until the sucking and discharging of the hot purified water is completed at least in the step of sucking and discharging the hot purified water from the bottom side of the container, particularly controlled and maintained at a temperature in the range of 30xc2x0 C. to 65xc2x0 C., and set at xe2x88x92350 to xe2x88x92150 mmHg in terms of degree of depressurization.
Further, Japanese Application No 11-183469 discloses (1) a surface dry processing method for drying a material such as a wafer and the like, by heating an organic solvent at a temperature of 60xc2x0 C. to 80xc2x0 C. and applying the heated organic solvent to a fluid surface, thereby forming a film including the organic solvent on the processed fluid surface by means of a drying bath for accommodating the wafer therein; (2) a processing fluid supply means for supplying processing fluid to the inside of the drying bath, (3) an organic solvent supply means for supplying a heated organic solvent in the drying bath; and (4) a vapor supply means for supplying vapor containing an organic solvent.
In the surface drying processing method particularly disclosed in Japanese Patent No. 3,017,033 and Japanese Application No. 11-183469, the surface of a wafer and the like is cleaned by a chemical fluid, rinsed by a processing fluid such as purified water and then dried by an organic solvent such as isopropyl alcohol (hereinafter referred to as xe2x80x9cIPAxe2x80x9d).
For example, when the wafer is exposed to a vapor of IPA after the wafer is cleaned by purified water, the IPA is condensed on the surface of the wafer. When the IPA is condensed, the purified water that has adhered to the wafer is replaced by the IPA, and contaminants such as particles and the like are washed out as the purified water runs from the surface of the wafer. Thereafter, when the IPA is vaporized, the surface of the wafer is dried. If a water droplet remains on the substrate surface during the drying process, an oxide film (hereinafter referred to as xe2x80x9cWatermarkxe2x80x9d) is formed on the substrate surface. Since the watermark causes the quality of the substrate to deteriorate, it is desirable to prevent as much as possible the adhesion of contaminants onto the substrate.
If a substrate (e.g., wafer) is processed by a chemical fluid, the surface condition of the substrate varies depending on the kind of processing applied. For example, the surface of a semiconductor wafer, becomes hydrophobic when processed by, e.g., hydrofluoric acid chemical fluid, and becomes hydrophilic when processed by a fluid other than hydrofluoric acid chemical fluid. In a conventional substrate processing unit, vapor is generated in the same condition irrespective of whether the substrate surface is hydrophobic or hydrophilic. However, according to the research of the inventors of the present application, the amount of contaminants that remain on the substrate after drying where the substrate surface is hydrophobic differs from such amount where the substrate surface is hydrophilic. The inventors have also ascertained that the amount of contaminants that adhere to the substrate is correlated with the amount of production of organic solvent vapor.
The object of the invention is to provide a substrate processing unit capable of reducing contaminants that adhere to a substrate surface as much as possible.
To achieve this, the substrate processing unit of the invention comprises (1) a processing bath for accommodating substrates to be processed; (2) a processing fluid supply means for supplying a processing fluid to the processing bath; (3) a vapor generating bath for accommodating an organic solvent and introducing the vapor generated from the organic solvent into the processing bath; (4) a processing fluid discharge means for discharging the processing fluid from the processing bath; and (5) a solvent heating unit for heating the organic solvent in the vapor generating bath, wherein the solvent heating unit heats the organic solvent at an initial temperature when the surface of each substrate accommodated in the processing bath is hydrophobic, and heats the organic solvent at a higher temperature when the substrate surface is hydrophilic.
According to the invention, when the substrate surface is hydrophobic, the organic solvent in the vapor generating bath is heated at an initial temperature. If the substrate surface is hydrophilic, the organic solvent in the vapor generating bath is heated at a relatively higher temperature. An organic solvent vapor is generated by supplying inert gas to the vapor generating bath, and it is introduced in the processing bath. The organic solvent heated at the higher temperature generates more vapor than organic solvent heated at the initial temperature. When the vapor is condensed on the substrate surface, a processing fluid (e.g., purified water) which has adhered to the substrate so far is replaced by the organic solvent, and the processing fluid runs from the substrate surface and accordingly, contaminants such as particles and the like are washed out. Thereafter, when the organic solvent is vaporized, the substrate surface is dried.
An example of the processing fluid is represented by purified water, and an example of the organic solvent is isopropyl alcohol. In this case, it is preferable that the initial temperature be in the range of 50xc2x0 C.xc2x15xc2x0 C. and the second temperature be in the range of 70xc2x0 C.xc2x15xc2x0 C.
The substrate processing unit of the invention may be provided with a first solvent heating bath for accommodating an organic solvent which is heated at the initial temperature, a second solvent heating bath for accommodating an organic solvent which is heated at the second temperature, a piping for connecting the first and second solvent heating baths and the vapor generating bath, and switching means provided on the piping for allowing the first solvent heating bath to communicate with the vapor generating bath where the surface of the substrate accommodated in the processing bath is hydrophobic, and for allowing the second solvent heating bath to communicate with the vapor generating bath where the surface of the substrate accommodated in the processing bath is hydrophilic.
Further, the substrate processing unit of the invention may be provided with inert gas supply means for supplying a first amount of inert gas for bubbling to the organic solvent in the vapor generating bath when the substrate surface is hydrophobic, and for supplying a second amount of inert gas for bubbling to the organic solvent in the vapor generating bath when the substrate surface is hydrophilic, wherein the second amount is larger than the first.
According to the invention, it is possible to prevent contaminants such as particles, watermarks and the like from being adhered to the substrate surface by controlling the amount of organic solvent vapor produced in response to a surface condition of the substrate, thereby obtaining a high quality substrate. Further, it is possible to prevent contaminants from being adhered to the substrate surface in response to the surface condition of the substrate, thereby obtaining a high quality substrate when drying the substrate which is cleaned by purified water through the use of IPA.
In addition, it is possible to prevent contaminants from being adhered to the substrate surface even under any condition of the substrate surface by keeping an IPA fluid in the vapor generating bath at a temperature in the range of 50xc2x0 C.xc2x15xc2x0 C. when the substrate surface is hydrophobic while keeping the IPA fluid at a temperature in the range of 70xc2x0 C.xc2x15xc2x0 C. when the substrate surface is hydrophilic. It is also possible to quickly supply the organic solvent at a temperature corresponding to the surface condition of the substrate to the vapor generating bath.
Moreover, it is possible to prevent contaminants from being adhered to the substrate surface by controlling the amount of production of the organic solvent vapor in response to the substrate surface condition, thereby obtaining a high quality substrate by supplying the processing bath with a desired chemical fluid suitable for processing the substrate.
Further, it is possible to continuously wash out contaminants, particles and the like inside the inner bath of the substrate processing unit by allowing the processing fluid supplied from the inner bath to flow into the outer bath to discharge the processing fluid from the outer bath.